The present invention relates generally to the field of downhole water separation, and more particularly, but not by way of limitation, to downhole water separation used in conjunction with submersible pumps.
Fluid separation systems are an important and expensive part of most hydrocarbon production facilities. The separation of fluids based on different properties is known in the industry. A variety of separation methods are used, including gravity separators, membrane separators and cyclone separators. Each of these separators uses a different technique to separate the fluids and each achieves a different efficiency depending upon the device and its application. Gravity separators, for instance, can be efficient when there is a great density difference between the two fluids and there are no space or time limitations. Another separator, the membrane separator, uses the relative diffusibility of fluids for separation. The membrane separator is not well suited to use with an electric submersible pump (ESP) due to the high flow rates and limited space.
Since electric submersible pumps are capable of producing fluids at high rates and pressures, such pumps are often used for downhole fluid movement including downhole fluid separation applications. Any separation method that is time dependant, such as the above mentioned gravity and membrane separators, do not work well with an electric submersible pump. Another separator, the hydrocyclone, on the other hand, has been used effectively with electric submersible pumps, both on the surface and below the surface. Hydrocyclone separators are non-rotating devices, using a specific geometric shape to induce fluid rotation. They create high g-forces in the fluids as the fluids spin though the device. This process results in the lighter fluids forming a core in the middle of the separator. This core is extracted out the topside of the hydrocyclone separator as the oil stream. The separated water is rejected from the opposite side. One problem associated with this method of separation is the excessive pressure drop in the fluid passing through the hydrocyclone.
This current method of separating fluids downhole has certain problems associated with it. First, a system design which incorporates an ESP with a hydrocyclone, is often complicated. Depending upon the relative location of the disposal and the production zones, these systems usually have one or two conduits running from the separator and pump to the respective zones or are limited on where they can be placed. These conduits not only cause excessive pressure drops but also are the weak links in the assembly, often causing mechanical problems during installation.
Secondly, a hydrocyclone separator is a non-rotating device. Since the separator can not rotate, special provisions have to be made in a separation system design for torque transmission above or below the separator. These provisions, which depend on the particular application and the location of the injection and production zones, further complicate the design of the separation system. Finally a hydrocyclone does not work well with free gas in the process stream. Free gas hinders the separation process in the hydrocyclone as is well known to those skilled in the art. This is also a problem when volatile oils are present as there is a pressure drop in the process stream as the volatile oil passes through the hydrocyclone, thereby forming free gas to be liberated and making separation difficult.
The present invention, overcoming these problems, provides a separation system using a rotary device in conjunction with standard ESP equipment.
The present invention includes a downhole rotary water separation system for the separation and transfer of different density fluids in downhole applications using a pump, motor, rotary separator and a shaft-incorporated packer, as necessary, with a minimum use of conduits. Since torque can be transferred between all moving components as well as the packer, system arrangement is not restricted to one in which the motor and pump must be directly above or below the separator.